I have a light fixture that just stays on when I turn the main power on. The switch will not turn it off. I do not have the red wires attached to anything.

Want to tell us more about this eternally burning light?
Did this failure to turn off just happen or did you make some changes to something?

I bought a new light fixture to install after taking out old and disposing it. And I also am replacing the light switch. I believe the problem is in the light switch wiring. I think I'm going to need a tester for the wires in the box. The house is about 40yrs old and the wiring is kind of jacked up. There are 2 switches and 2 light fixtures. 1 switch should operate 1 fixture right now both switches operate 1 fixture.

Yep, we need to know more info. Is this an outside "farm type" light?

It's an inside light. 1 switch controls outside light and the other switch controls light fixture in kitchen. Both switches are in the same box.

"1 switch should operate 1 fixture right now both switches operate 1 fixture." this puts the problem on you and how you connected the wires to the switches. I am still trying to picture in my mind how you could have done this but the original wiring would not be capable of sending power to one fixture from both switches. Do you have any "spare" wires in this switch box that are not connected to anything?

I do not have the red wires attached to anything

That indicates that you possibly miswired the light fixture.

Tell us what wires you have in the ceiling box and the switch box.

Tell us like this,

I have one two wire cable (black and white)
Or
I have 3 two wire cables (black and white) and one 3-wire cable (black, red, white) in the box.

I have three black wires and three white wires. I connected the new fixture black to black and white to white. There was a 4 foot flourecent in place before. The new light stays on as soon as I connect the wires. The wall switch will not turn it off. There are no other wires in the ceiling box.
Roland

I have three black wires and three white wires. I connected the new fixture black to black and white to white. There was a 4 foot flourecent in place before. The new light stays on as soon as I connect the wires. The wall switch will not turn it off. There are no other wires in the ceiling box.
Roland
How was it wired before? That's how you should wire it now.

Turn breaker off. Take note of all things that work with the breaker on and do not work with the breaker off.

Disconnect all wires.

Make sure wall switch is in the off position.

Pick two black wires and connect them together with a wire nut. Connect the white wires (in the same cables with the black wires) together with a wire nut. Call these cables A and B. Leave the other cable, call it cable C, unconnected but put wire nuts on each wire.

Turn on breaker. Do not turn on wall switch.

If everything that was working before is now working, you have connected the power coming into the ceiling box to the power going out of the ceiling box.

If things do not work, turn off breaker. Disconnect cables A and B. Connect the black and white wires of cable A to the black and white wires of cable C.

Turn on breaker. If everything works you have connected the power in to the power out.

If things do not work turn breaker off and connect cable B to cable C.

One of these three combinations should connect the power in to the power out.

When you have found the correct combination for the power in to power out connection, put a piece of black electricians tape on the end of the remaining, unconnected white wire. Connect that remaining white wire (with the black tape) to the blacks of the power in/power out cables. That white wire will take power to the switch. The black in that cable will return power from the switch when the switch is in the on position.

Install the new light fixture by connecting the white of the fixture to the white of the power in/ power out connection. Connect the black of the fixture to the remaining unconnected black.